Within gas turbine engines the leading edges of rotating and stationary aerofoils and of other components are subject to high levels of erosion and impact loading. In particular the fan blades and their subsequent guide vanes can experience harsh abrading environments including dust, sand, ice and water. They can also suffer impacts from foreign bodies such as birds and debris. Therefore the leading edges need to be sufficiently resistant to withstand such environments and impacts.
In respect of a metallic component, the metal of component itself may be sufficiently resistant, or a surface coating can be added that improves resistance. However, in general, polymer matrix composite materials, such as sometimes are used to form fan blades and guide vanes, are not sufficiently resistant to prevent erosion or impact damage. A particular danger is then that leading edge damage in components formed of these materials can grow into the more structural parts of the components.
One proposed solution is to wrap a metal sheath protector around the leading edge. This gives protection against erosion and impact damage, and makes it possible to dress back the leading edge.
When fixing a metal sheath protector at the leading edge it is usually necessary to apply respective surface treatments to the sheath and the component, and then to bond the two together. However, being bonded, the metallic leading edges have a tendency to detach during high energy impact events, and release from the component. This is especially an issue on rotating components, such as the fan blades. When a metal leading edge sheath protector releases from a fan blade it can form a high energy spear that can be difficult to contain in the engine casing, or, if directed forward, can cause a serious threat to the aircraft.
In addition, the shapes and tolerances required of metal leading edge sheath protectors can cause significant problems during manufacture. In particular, due to their complex form, pressing and rolling type manufacturing methods are difficult to control with sufficient accuracy. Machining operations are complicated by access issues to internal features of the parts. Welding can cause significant distortion problems due to the relative thinness and flexibility of the protectors.